I love Rockford, but I find it implausible that he would put $10K in a stranger's safe. All of a sudden people know he's got valuables, and he can't get his money back without cooperation. Even I'm smarter than this... It makes more sense to stay in the motel, keep a low profile, keep the cash in your pocket, and be on your way the next day.
Secondly, how could he have gotten the Sheriff to cooperate in his sting at the lake? The Sheriff believed him to be guilty of murder, plus Jim escaped from a jail cell and stole a police car. If that Sheriff had known Jim's whereabouts he'd have been in jail in a flash.
And that microphone wouldn't have picked up a thing at that distance, with the wind blowing.